There presently exists apparatus for the production of spunbond webs or fabrics formed from filaments or fibers typically made from a thermoplastic resin. Such an apparatus is disclosed in U.S. Pat. No. 5,814,349 issued Sep. 29, 1998, the disclosure of which is incorporated herein by reference. Typically, such apparatus includes a spinneret for producing a curtain of strands and a process-air blower for blowing process air onto the curtain of strands for cooling same to form thermoplastic filaments. The thermoplastic filaments are then typically, aerodynamically entrained by the process air for aerodynamic stretching of the thermoplastic filaments which are then, after passing through a diffuser, deposited upon a continuously circulating sieve belt for collecting the interentangled filaments and forming a web thereon. The web or fabric, so formed, is then subject to further processing.
In the spunbonding process for manufacturing nonwoven materials, thermoplastic fiber forming polymer is placed in an extruder and passed through a linear or circular spinneret. The extruded polymer streams are rapidly cooled and attenuated by air and/or mechanical drafting rollers to form desired diameter solidifying filaments. The solidifying filaments are then laid down on a conveyor belt to form a web. The web is then bonded by rollers to form a spunbonded web.
In the meltblown process for manufacturing nonwoven materials, thermoplastic forming polymer is placed in an extruder and is then passed through a linear die containing about twenty to forty small orifices per inch of die width. Convergent streams of hot air rapidly attenuate the extruded polymer steams to form solidifying filaments. The solidifying filaments are subsequently blown by high velocity air onto a take-up screen or another layer of woven or nonwoven material thus forming a meltblown web.
The spunbonding and meltblowing process can be combined in applications such as SMS shown in FIG. 1. In SMS a first layer of spunbonded material is formed on a belt or conveyor 10 by the spunbond beam 12. The belt 10 typically has a uniform surface and air permeability to reach the right formation during spunbond process. The spunbonded material is deposited on the belt 10 at a point between the upstream and downstream press rolls 16 and 16′ to form the web. The press rolls 16 and 16′ function to eliminate any air leakage between the belt 10 and the web to enhance pre-bonding caused by the pressure and temperature of the top heated press roll. In order to assist in drawing the thermoplastic fibers onto the belt 10, a vacuum box 14 is located beneath the belt 10 and which applies a suction to the belt. The airflow needed for the spunbond process is sucked from the system by a vacuum box 14.
Next, in the meltblown beam 18 small fibers are blown onto the spunbond web layer. During the meltblowing process there is typically no need for precompaction press rolls.
Finally, a second spunbond beam 20 with press rolls 22 applies a second spunbond layer onto the web formed of the meltblown layer and the first spunbond layer. The composite spunbond-meltblown-spunbond material is then consolidated through a calender or a dryer mechanism (not shown).
While, initially it may appear that to form a pattern on an SMS or spunbond product all that would be necessary is a conveyor or forming belt having the desired topographical features, it is intuitive that the combination of the press rolls and the thermoplastic materials could be combined to create a spunbond material having a mirror image of the pattern of the conveyor. However, as described in U.S. Patent Application No. 2003/0164199, incorporated herein by reference, the competing factors of speed, avoidance of undesirable marking, air permeability, and reduced bounce make the use of a topographical pattern belt as the conveyor very difficult in practice.
There have also been described in the art other methods of providing patterns onto a nonwoven web or preform. For example, reference is made to U.S. Pat. No. 5,115,544, the disclosure of which is incorporated herein by reference. In the '544 patent, there is described a spunlacing method and apparatus for imprinting a pattern on a nonwoven material. In particular, the '544 patent describes a method and apparatus for imprinting a pattern on nonwovens formed by a spunlacing technique. As described therein, a nonwoven material is formed and transported on a wire screen having a pattern. The nonwoven material is then treated by a series of water jets, which cause the nonwoven to assume the shape of the wire screen. In this way the pattern from the wire screen is imparted on the nonwoven resulting in a patterned nonwoven.
While this method has proven to be very satisfactory in a spunlace application, the present invention is directed towards a spunbond apparatus and process. Accordingly, there is a need for an apparatus and method for the production of patterned spunbond nonwovens, and particularly an apparatus and method for the production of patterned SMS nonwoven.